This work is designed to understand how the presence of helper and suppressor thymic-derived cells (T-cells) effect the delayed-type-hypersensitivity (DTH) skin reaction. This study uses azobenezene-arsonate-N-chloroacetyl-tyrosine (ABA-T) as the determinant being recognized by the regulatory T-cells. The ABA-T determinant is covalently bonded to human-gamma-globulin (HGG). This coupling permits regulatory T-cells, specific for ABA-T, to control the DTH skin response to HGG. The regulation is being studied in vivo and in vitro.